Aldehydes such as acrolein emitted by combustion sources are often associated with respirable sized particles. The majority of this hydrophilic vapor is absorbed in the upper respiratory tract. However, if acrolein is absorbed on respirable particles which are deposited in the distal lung, the toxic site is shifted from the upper to the lower respiratory tract. The overall goal of this proposal is to determine the mechanisms by which the acrolein-carbonaceous particle complex compromises the defenses of the lungs. The hypothesis of this application is that acrolein must be bound to the surface of a particle to exhibit pulmonary toxicity. The hypothesis of this application is based on the assumption that release of particle-bound acrolein (bioavailability) is required in order to produce the subsequent bioeffects. This aim will be accomplished through studies of specific functional parameters of lung defenses, determination of acute and long-term lung toxicity and the mechanisms that govern the toxic effects of acrolein-- particle complexes.